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Moving objects can become even sharper if each frame is displayed in a fixed location for a shorter period of time (reduced MPRT), preventing eye-tracking motio

Moving objects can become even sharper if each frame is displayed in a fixed location for a shorter period of time (reduced MPRT), preventing eye-tracking motion from smearing each displayed frame. This can be achieved through CRT/OLED scanout (often rolling) or LCD backlight strobing (usually full-frame by necessity). Unfortunately displaying each frame for a short time is unbearably flickery at 24 Hz (so movie projectors would show film frames 2-3 times), just barely tolerable at 50 (to the point some European CRT televisions frame-doubled 50 Hz video to 100 Hz, causing objects to appear doubled in motion), and ideally needs 70-75 Hz or above for optimally fluid motion and minimum eyestrain (which can't show 60 FPS recorded video without judder and/or tearing).

s4i 3y ago
> to the point some European CRT televisions frame-doubled 50 Hz video to 100 Hz, causing objects to appear doubled in motion Hmm, this is not accurate (or I don't understand what you mean). 100Hz CRT TVs available in the 90s/00s did not interpolate frames to get smoother motion – they only existed to reduce flicker. I think such TVs also existed in NTSC markets (120Hz)? Anyway, ever since the late 00s, pretty much all the TVs you can buy from a store do come with an interpolation algorithm to artificially display a higher frame rate image (e.g. 100Hz/120Hz) from a lower frame rate source (e.g. 23.976/24/29.97/30/50/59.94/60 fps) – which (personal opinion) looks terrible (and can be turned off from the settings – but the default is always on). This is an interesting side tangent when it comes to motion blur, because the blur is prebaked in the input signal and cannot be easily removed. Thus, the end result always has an artificial look. For instance, if the source material is shot in 24fps with the typical 180 degree shutter angle, each frame spans 41.6ms of which the shutter was open for 20.8ms. Then your TV interpolates that to be 96Hz or whatever. However, the individual output frames still look (or, with the added artifacts etc., mostly look) like the shutter was open for 20.8ms per frame. However, each frame now spans 10.2ms which is a shorter time than the shutter speed!
- cubefox 3y ago
  As far as I understand, you get doubling not because of any interpolation but because you track objects with your eye. That means the tracked object is in rest in your vision. Which means the screen actually moves relative to your vision. Which means the object smears, where the pixel length of the smear is equal to the pixel distance the tracked object moves in the time the frame is visible on screen. On CRT there is less smear, because the frames are only flashed for a short time on the otherwise dark screen. But if the FPS are not equal to the display Hz, e.g. a half, the tracked object appears on multiple, e.g. two, locations on the screen. Because you show the frame twice, and if you track an object, the screen has moved (relative to your vision) for a few pixels by the time you show the second frame. This happens e.g. if you play a 30 FPS game on a 60 Hz CRT, or when you watch 50 FPS content on a 100 Hz screen. Though the effect isn't usually as dramatic as it may sound here. Doubling is also not as bad as smearing, e.g. in the case of scrolling text.
cubefox 3y ago
Double images are already present in NTSC/PAL due to interlacing. So when doubling the Hz of PAL on a CRT, you get a quadruple image. Though this probably still looks better than non-interlaced content on LCD/OLED, which exhibits smearing instead.
- mrob 3y ago
  Double images are only present in converted film content, which in the case of PAL is done by speeding it up from 24fps to 25fps, and splitting each frame into two fields. In the case of native PAL video content, each interlaced field shows image data from a different time, so you don't see double images.
  - cubefox 3y ago
    In case of PAL video we don't see two duplicate frames, but we still see two different frames (fields) at the same time. That's the "double image" I meant.
    - mrob 3y ago
      On an interlaced display, the two different fields are not displayed at the same time. If you merge the two fields into a single non-interlaced frame and display it on a progressive scan display you might see a double image, but that's not inherent to interlaced video.

s4i 3y ago

> to the point some European CRT televisions frame-doubled 50 Hz video to 100 Hz, causing objects to appear doubled in motion Hmm, this is not accurate (or I don't understand what you mean). 100Hz CRT TVs available in the 90s/00s did not interpolate frames to get smoother motion – they only existed to reduce flicker. I think such TVs also existed in NTSC markets (120Hz)? Anyway, ever since the late 00s, pretty much all the TVs you can buy from a store do come with an interpolation algorithm to artificially display a higher frame rate image (e.g. 100Hz/120Hz) from a lower frame rate source (e.g. 23.976/24/29.97/30/50/59.94/60 fps) – which (personal opinion) looks terrible (and can be turned off from the settings – but the default is always on). This is an interesting side tangent when it comes to motion blur, because the blur is prebaked in the input signal and cannot be easily removed. Thus, the end result always has an artificial look. For instance, if the source material is shot in 24fps with the typical 180 degree shutter angle, each frame spans 41.6ms of which the shutter was open for 20.8ms. Then your TV interpolates that to be 96Hz or whatever. However, the individual output frames still look (or, with the added artifacts etc., mostly look) like the shutter was open for 20.8ms per frame. However, each frame now spans 10.2ms which is a shorter time than the shutter speed!

cubefox 3y ago
As far as I understand, you get doubling not because of any interpolation but because you track objects with your eye. That means the tracked object is in rest in your vision. Which means the screen actually moves relative to your vision. Which means the object smears, where the pixel length of the smear is equal to the pixel distance the tracked object moves in the time the frame is visible on screen. On CRT there is less smear, because the frames are only flashed for a short time on the otherwise dark screen. But if the FPS are not equal to the display Hz, e.g. a half, the tracked object appears on multiple, e.g. two, locations on the screen. Because you show the frame twice, and if you track an object, the screen has moved (relative to your vision) for a few pixels by the time you show the second frame. This happens e.g. if you play a 30 FPS game on a 60 Hz CRT, or when you watch 50 FPS content on a 100 Hz screen. Though the effect isn't usually as dramatic as it may sound here. Doubling is also not as bad as smearing, e.g. in the case of scrolling text.

cubefox 3y ago

Double images are already present in NTSC/PAL due to interlacing. So when doubling the Hz of PAL on a CRT, you get a quadruple image. Though this probably still looks better than non-interlaced content on LCD/OLED, which exhibits smearing instead.

mrob 3y ago
Double images are only present in converted film content, which in the case of PAL is done by speeding it up from 24fps to 25fps, and splitting each frame into two fields. In the case of native PAL video content, each interlaced field shows image data from a different time, so you don't see double images.
- cubefox 3y ago
  In case of PAL video we don't see two duplicate frames, but we still see two different frames (fields) at the same time. That's the "double image" I meant.
  - mrob 3y ago
    On an interlaced display, the two different fields are not displayed at the same time. If you merge the two fields into a single non-interlaced frame and display it on a progressive scan display you might see a double image, but that's not inherent to interlaced video.